Halogenated compounds have long been used as flame retardant additives in organic materials which would normally burn in air when contacted with an ignition source. One such additive is polybrominated diphenyl ether which can be made by adding diphenyl ether to bromine containing a catalyst such as aluminum chloride at temperatures above 35.degree. C. according to U.S. Pat. No. 4,287,373. A related process that can be used to perbrominate benzene, toluene, phenol, xylene, biphenyl, biphenyl ether or biphenyl sulfide is shown in U.S. Pat. No. 3,965,197. Similar halogenated polyphenylene oxides are described in U.S. Pat. No. 3,760,003. These are made by the slow addition of bromine to a polyphenylene oxide containing a catalyst such as iron powder.